boil up vs heat up

boil up

verb
  • To become more excited, intense or exciting. 

  • To cook or prepare by boiling. 

noun
  • A traditionally Maori soup/stew made with potatoes, pork and other ingredients. 

heat up

verb
  • To become more exciting or intense. 

  • To heat, to cause to become hotter. 

How often have the words boil up and heat up occurred in a corpus of books? (source: Google Ngram Viewer )